diff --git a/.gitignore b/.gitignore
index 1e7a1e198..02387abda 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,4 +17,5 @@ local_build/*compiler*.jar
 local_build/local_*_compressed.js
 chromedriver
 typings/tmp/*
+build/
 dist/
diff --git a/gulpfile.js b/gulpfile.js
index 3f0dc46a4..53a756874 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -23,6 +23,7 @@ var cleanupTasks = require('./scripts/gulpfiles/cleanup_tasks');
 module.exports = {
   deployDemos: appengineTasks.deployDemos,
   default: buildTasks.build,
+  generateLangfiles: buildTasks.generateLangfiles,
   build: buildTasks.build,
   buildCore: buildTasks.core,
   buildBlocks: buildTasks.blocks,
@@ -31,11 +32,17 @@ module.exports = {
   buildCompressed: buildTasks.compressed,
   buildGenerators: buildTasks.generators,
   buildAdvancedCompilationTest: buildTasks.advancedCompilationTest,
+  checkin: gulp.parallel(buildTasks.checkinBuilt, typings.checkinTypings),
+  checkinBuilt: buildTasks.checkinBuilt,
+  clean: gulp.parallel(buildTasks.cleanBuildDir, packageTasks.cleanReleaseDir),
+  cleanBuildDir: buildTasks.cleanBuildDir,
+  cleanReleaseDir: packageTasks.cleanReleaseDir,
   gitSyncDevelop: gitTasks.syncDevelop,
   gitSyncMaster: gitTasks.syncMaster,
   gitCreateRC: gitTasks.createRC,
   gitUpdateGithubPages: gitTasks.updateGithubPages,
   typings: gulp.series(typings.typings, typings.msgTypings),
+  checkinTypings: typings.checkinTypings,
   package: packageTasks.package,
   checkLicenses: licenseTasks.checkLicenses,
   recompile: releaseTasks.recompile,
diff --git a/msg/messages.js b/msg/messages.js
index a142f6fe9..636de4bd5 100644
--- a/msg/messages.js
+++ b/msg/messages.js
@@ -8,13 +8,15 @@
  * @fileoverview English strings.
  * @author fraser@google.com (Neil Fraser)
  *
- * After modifying this file, either run "npm run build:langfiles" from the
- * parent directory, or run (from this directory):
- * ../scripts/i18n/js_to_json.py
- * to regenerate json/{en,qqq,synonyms}.json.
+ * After modifying this file, run:
+ *
+ *     npm run generate:langfiles
+ *
+ * to regenerate json/{en,qqq,constants,synonyms}.json.
  *
  * To convert all of the json files to .js files, run:
- * ../scripts/i18n/create_messages.py json/*.json
+ *
+ *     npm run build:langfiles
  */
 'use strict';
 
diff --git a/package.json b/package.json
index e83f97aa9..75d294dc0 100644
--- a/package.json
+++ b/package.json
@@ -29,13 +29,19 @@
     "build:langfiles": "gulp buildLangfiles",
     "build:uncompressed": "gulp buildUncompressed",
     "bump": "npm --no-git-tag-version version 4.$(date +'%Y%m%d').0",
+    "clean": "gulp clean",
+    "clean:build": "gulp cleanBuildDir",
+    "clean:release": "gulp cleanReleaseDir",
+    "checkin": "gulp checkin",
+    "checkin:built": "gulp checkinBuilt",
+    "checkin:typings": "gulp checkinTypings",
     "deployDemos": "gulp deployDemos",
     "format": "git-clang-format",
     "format:sortrequires": "gulp sortRequires",
+    "generate:langfiles": "gulp generateLangfiles",
     "license": "gulp checkLicenses",
     "lint": "eslint .",
     "package": "gulp package",
-    "prepare": "npm run package",
     "prepareDemos": "gulp prepareDemos",
     "publish": "gulp publish",
     "publish:beta": "gulp publishBeta",
diff --git a/scripts/gulpfiles/appengine_tasks.js b/scripts/gulpfiles/appengine_tasks.js
index 66573d3f5..5e3f7d681 100644
--- a/scripts/gulpfiles/appengine_tasks.js
+++ b/scripts/gulpfiles/appengine_tasks.js
@@ -47,8 +47,8 @@ function copyStaticSrc(done) {
  */
 function copyAppengineSrc() {
   const appengineSrc = [
-      path.join(demoStaticTmpDir, 'appengine/**/*'),
-      path.join(demoStaticTmpDir, 'appengine/.gcloudignore'),
+      `${demoStaticTmpDir}/appengine/**/*`,
+      `${demoStaticTmpDir}/appengine/.gcloudignore`,
   ];
   return gulp.src(appengineSrc).pipe(gulp.dest(demoTmpDir));
 }
diff --git a/scripts/gulpfiles/build_tasks.js b/scripts/gulpfiles/build_tasks.js
index 6553e8872..b27d21a5b 100644
--- a/scripts/gulpfiles/build_tasks.js
+++ b/scripts/gulpfiles/build_tasks.js
@@ -21,8 +21,10 @@ var through2 = require('through2');
 var closureCompiler = require('google-closure-compiler').gulp();
 var closureDeps = require('google-closure-deps');
 var argv = require('yargs').argv;
-var { getPackageJson } = require('./helper_tasks');
+var rimraf = require('rimraf');
 
+var {BUILD_DIR} = require('./config');
+var {getPackageJson} = require('./helper_tasks');
 
 ////////////////////////////////////////////////////////////
 //                        Build                           //
@@ -217,7 +219,7 @@ function buildCompressed() {
       }))
       .pipe(
           gulp.sourcemaps.write('.', {includeContent: false, sourceRoot: './'}))
-      .pipe(gulp.dest('./'));
+      .pipe(gulp.dest(BUILD_DIR));
 };
 
 /**
@@ -242,7 +244,7 @@ function buildBlocks() {
       includeContent: false,
       sourceRoot: './'
     }))
-    .pipe(gulp.dest('./'));
+    .pipe(gulp.dest(BUILD_DIR));
 };
 
 /**
@@ -268,7 +270,7 @@ function buildGenerator(language, namespace) {
       includeContent: false,
       sourceRoot: './'
     }))
-    .pipe(gulp.dest('./'));
+    .pipe(gulp.dest(BUILD_DIR));
 };
 
 /**
@@ -408,31 +410,59 @@ goog.require('Blockly.requires');
   });
 };
 
+/**
+ * This task regenrates msg/json/en.js and msg/json/qqq.js from
+ * msg/messages.js.
+ */
+function generateLangfiles(done) {
+  // Run js_to_json.py
+  const jsToJsonCmd = `python scripts/i18n/js_to_json.py \
+      --input_file ${path.join('msg', 'messages.js')} \
+      --output_dir ${path.join('msg', 'json')} \
+      --quiet`;
+  execSync(jsToJsonCmd, { stdio: 'inherit' });
+
+  console.log(`
+Regenerated several flies in msg/json/.  Now run
+
+    git diff msg/json/*.json
+
+and check that operation has not overwritten any modifications made to
+hints, etc. by the TranslateWiki volunteers.  If it has, backport
+their changes to msg/messages.js and re-run 'npm run generate:langfiles'.
+
+Once you are satisfied that any new hints have been backported you may
+go ahead and commit the changes, but note that the generate script
+will have removed the translator credits - be careful not to commit
+this removal!
+`);
+
+  done();
+};
+
 /**
  * This task builds Blockly's lang files.
  *     msg/*.js
  */
 function buildLangfiles(done) {
-  // Run js_to_json.py
-  const jsToJsonCmd = `python ./scripts/i18n/js_to_json.py \
---input_file ${path.join('msg', 'messages.js')} \
---output_dir ${path.join('msg', 'json')} \
---quiet`;
-  execSync(jsToJsonCmd, { stdio: 'inherit' });
-
-  // Run create_messages.py
+  // Create output directory.
+  // TODO(#5000): does mkidr -p work on Windows?
+  const outputDir = path.join(BUILD_DIR, 'msg', 'js');
+  execSync(`mkdir -p ${outputDir}`, {stdio: 'inherit'});
+  
+  // Run create_messages.py.
   let json_files = fs.readdirSync(path.join('msg', 'json'));
   json_files = json_files.filter(file => file.endsWith('json') &&
-    !(new RegExp(/(keys|synonyms|qqq|constants)\.json$/).test(file)));
+      !(new RegExp(/(keys|synonyms|qqq|constants)\.json$/).test(file)));
   json_files = json_files.map(file => path.join('msg', 'json', file));
   const createMessagesCmd = `python ./scripts/i18n/create_messages.py \
   --source_lang_file ${path.join('msg', 'json', 'en.json')} \
   --source_synonym_file ${path.join('msg', 'json', 'synonyms.json')} \
   --source_constants_file ${path.join('msg', 'json', 'constants.json')} \
   --key_file ${path.join('msg', 'json', 'keys.json')} \
-  --output_dir ${path.join('msg', 'js')} \
+  --output_dir ${outputDir} \
   --quiet ${json_files.join(' ')}`;
-    execSync(createMessagesCmd, { stdio: 'inherit' });
+  execSync(createMessagesCmd, {stdio: 'inherit'});
 
   done();
 };
@@ -510,13 +540,40 @@ const build = gulp.parallel(
   buildLangfiles
 );
 
+/**
+ * This task copies built files from BUILD_DIR back to the repository
+ * so they can be committed to git.
+ */
+function checkinBuilt() {
+  return gulp.src([
+    `${BUILD_DIR}/**.js`,
+    `${BUILD_DIR}/**.js.map`,
+    `${BUILD_DIR}/**/**.js`,
+    `${BUILD_DIR}/**/**.js.map`,
+  ]).pipe(gulp.dest('.'));
+};
+
+/**
+ * This task cleans the build directory (by deleting it).
+ */
+function cleanBuildDir(done) {
+  // Sanity check.
+  if (BUILD_DIR === '.' || BUILD_DIR === '/') {
+    throw new Error(`Refusing to rm -rf ${BUILD_DIR}`);
+  }
+  rimraf(BUILD_DIR, done);
+}
+
 module.exports = {
   build: build,
   core: buildCore,
   blocks: buildBlocks,
+  generateLangfiles: generateLangfiles,
   langfiles: buildLangfiles,
   uncompressed: buildUncompressed,
   compressed: buildCompressed,
   generators: buildGenerators,
+  checkinBuilt: checkinBuilt,
+  cleanBuildDir: cleanBuildDir,
   advancedCompilationTest: buildAdvancedCompilationTest,
 }
diff --git a/scripts/gulpfiles/config.js b/scripts/gulpfiles/config.js
new file mode 100644
index 000000000..8f8424c6c
--- /dev/null
+++ b/scripts/gulpfiles/config.js
@@ -0,0 +1,28 @@
+/**
+ * @license
+ * Copyright 2021 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @fileoverview Common configuration for Gulp scripts.
+ */
+
+var path = require('path');
+
+// Paths are all relative to the repository root.  Do not include
+// trailing slash.
+//
+// TODO(#5007): If you modify these values, you must also modify the
+// corresponding values in the following files:
+// 
+// - tests/scripts/compile_typings.sh
+// - tests/scripts/check_metadata.sh
+module.exports = {
+  // Directory to write compiled output to.
+  BUILD_DIR: 'build',
+
+  // Directory in which to assemble (and from which to publish) the
+  // blockly npm package.
+  RELEASE_DIR: 'dist',
+};
diff --git a/scripts/gulpfiles/git_tasks.js b/scripts/gulpfiles/git_tasks.js
index f08ab9e00..bfc28df4c 100644
--- a/scripts/gulpfiles/git_tasks.js
+++ b/scripts/gulpfiles/git_tasks.js
@@ -103,7 +103,9 @@ const updateGithubPages = gulp.series(
     execSync('git reset --hard upstream/develop', { stdio: 'inherit' });
     done();
   },
+  buildTasks.cleanBuildDir,
   buildTasks.build,
+  buildTasks.checkinBuilt,
   function(done) {
     execSync('git commit -am "Rebuild"', { stdio: 'inherit' });
     execSync('git push ' + upstream_url + ' gh-pages --force', { stdio: 'inherit' });
diff --git a/scripts/gulpfiles/package_tasks.js b/scripts/gulpfiles/package_tasks.js
index bf79b7a6e..6b791d2e6 100644
--- a/scripts/gulpfiles/package_tasks.js
+++ b/scripts/gulpfiles/package_tasks.js
@@ -17,13 +17,12 @@ gulp.umd = require('gulp-umd');
 
 var path = require('path');
 var fs = require('fs');
-var { getPackageJson } = require('./helper_tasks');
-
-const blocklyRoot = '../../';
-
-// The destination path where all the NPM distribution files will go.
-const packageDistribution = 'dist';
+var rimraf = require('rimraf');
+var {getPackageJson} = require('./helper_tasks');
+var {BUILD_DIR, RELEASE_DIR} = require('./config');
 
+// Path to template files for gulp-umd.
+const TEMPLATE_DIR = 'scripts/package/templates';
 
 /**
  * A helper method for wrapping a file into a Universal Module Definition.
@@ -35,7 +34,7 @@ function packageUMD(namespace, dependencies) {
     dependencies: function () { return dependencies; },
     namespace: function () { return namespace; },
     exports: function () { return namespace; },
-    template: path.join(__dirname, `${blocklyRoot}/scripts/package/templates/umd.template`)
+    template: path.join(TEMPLATE_DIR, 'umd.template')
   });
 };
 
@@ -49,26 +48,61 @@ function packageCommonJS(namespace, dependencies) {
     dependencies: function () { return dependencies; },
     namespace: function () { return namespace; },
     exports: function () { return namespace; },
-    template: path.join(__dirname, `${blocklyRoot}/scripts/package/templates/node.template`)
+    template: path.join(TEMPLATE_DIR, 'node.template')
   });
 };
 
+// Sanity check that the BUILD_DIR directory exists, and that certain
+// files are in it.
+function checkBuildDir(done) {
+  // Check that directory exists.
+  if (!fs.existsSync(BUILD_DIR)) {
+    done(new Error(`The ${BUILD_DIR} directory does not exist.  ` +
+        'Have both packageTasks.build and typingsTasks.typings been run?'));
+    return;
+  }
+  // Check files built by buildTasks.build exist in BUILD_DIR.
+  for (const fileName of [
+    'blockly_compressed.js',  // buildTasks.buildCompressed
+    'blocks_compressed.js',  // buildTasks.buildBlocks
+    'javascript_compressed.js',  // buildTasks.buildGenerators
+    'msg/js/en.js',  // buildTaks.buildLangfiles
+  ]) {
+    if (!fs.existsSync(`${BUILD_DIR}/${fileName}`)) {
+      done(new Error(
+          `Your ${BUILD_DIR} directory does not contain ${fileName}.  ` +
+          'Has packageTasks.build been run?  Try "npm run build".'));
+      return;
+    }
+  }
+  // Check files built by typings.typings exist in BUILD_DIR.
+  for (const fileName of ['blockly.d.ts', 'msg/en.d.ts']) {
+    if (!fs.existsSync(`${BUILD_DIR}/${fileName}`)) {
+      done(new Error(
+          `Your ${BUILD_DIR} directory does not contain ${fileName}.  ` +
+          'Has typings.typings been run?  Try "npm run typings".'));
+      return;
+    }
+  }
+  done();
+}
+
 /**
- * This task copies source files into the distribution directory.
+ * This task copies source files into the release directory.
  */
 function packageSources() {
   return gulp.src(['core/**/**.js', 'blocks/**.js', 'generators/**/**.js'],
       {base: '.'})
-    .pipe(gulp.dest(packageDistribution));
+    .pipe(gulp.dest(RELEASE_DIR));
 };
 
 /**
- * This task copies the compressed files and their source maps into the
- * distribution directory.
+ * This task copies the compressed files and their source maps into
+ * the release directory.
  */
 function packageCompressed() {
-  return gulp.src('*_compressed.js?(.map)')
-    .pipe(gulp.dest(packageDistribution));
+  return gulp.src('*_compressed.js?(.map)', {cwd: BUILD_DIR})
+    .pipe(gulp.dest(RELEASE_DIR));
 };
 
 /**
@@ -83,7 +117,7 @@ function packageBlockly() {
         cjs: './blockly_compressed',
       }]))
     .pipe(gulp.rename('blockly.js'))
-    .pipe(gulp.dest(packageDistribution));
+    .pipe(gulp.dest(RELEASE_DIR));
 };
 
 /**
@@ -98,7 +132,7 @@ function packageBlocks() {
         cjs: './blocks_compressed',
       }]))
     .pipe(gulp.rename('blocks.js'))
-    .pipe(gulp.dest(packageDistribution));
+    .pipe(gulp.dest(RELEASE_DIR));
 };
 
 /**
@@ -115,7 +149,7 @@ function packageIndex() {
         cjs: './node',
       }]))
     .pipe(gulp.rename('index.js'))
-    .pipe(gulp.dest(packageDistribution));
+    .pipe(gulp.dest(RELEASE_DIR));
 };
 
 /**
@@ -147,7 +181,7 @@ function packageBrowser() {
         cjs: './javascript',
       }]))
     .pipe(gulp.rename('browser.js'))
-    .pipe(gulp.dest(packageDistribution));
+    .pipe(gulp.dest(RELEASE_DIR));
 };
 
 /**
@@ -166,7 +200,7 @@ function packageCore() {
         cjs: './blockly',
       }]))
     .pipe(gulp.rename('core-browser.js'))
-    .pipe(gulp.dest(packageDistribution));
+    .pipe(gulp.dest(RELEASE_DIR));
 };
 
 /**
@@ -205,7 +239,7 @@ function packageNode() {
         cjs: './dart',
       }]))
     .pipe(gulp.rename('node.js'))
-    .pipe(gulp.dest(packageDistribution));
+    .pipe(gulp.dest(RELEASE_DIR));
 };
 
 /**
@@ -224,7 +258,7 @@ function packageNodeCore() {
         cjs: './blockly',
       }]))
     .pipe(gulp.rename('core.js'))
-    .pipe(gulp.dest(packageDistribution));
+    .pipe(gulp.dest(RELEASE_DIR));
 };
 
 /**
@@ -245,7 +279,7 @@ function packageGenerator(file, rename, namespace) {
         cjs: `./${file}`,
       }]))
     .pipe(gulp.rename(rename))
-    .pipe(gulp.dest(packageDistribution));
+    .pipe(gulp.dest(RELEASE_DIR));
 };
 
 /**
@@ -289,12 +323,12 @@ function packagePHP() {
 };
 
 /**
- * This task wraps each of the msg/js/* files into a UMD module.
+ * This task wraps each of the ${BUILD_DIR}/msg/js/* files into a UMD module.
  * @example import * as En from 'blockly/msg/en';
  */
 function packageLocales() {
   // Remove references to goog.provide and goog.require.
-  return gulp.src('msg/js/*.js')
+  return gulp.src(`${BUILD_DIR}/msg/js/*.js`)
       .pipe(gulp.replace(/goog\.[^\n]+/g, ''))
       .pipe(gulp.insert.prepend(`
       var Blockly = {};Blockly.Msg={};`))
@@ -303,7 +337,7 @@ function packageLocales() {
           amd: '../core',
           cjs: '../core',
         }]))
-      .pipe(gulp.dest(`${packageDistribution}/msg`));
+      .pipe(gulp.dest(`${RELEASE_DIR}/msg`));
 };
 
 /**
@@ -314,84 +348,111 @@ function packageLocales() {
  */
 function packageUMDBundle() {
   var srcs = [
-    'blockly_compressed.js',
-    'msg/js/en.js',
-    'blocks_compressed.js',
-    'javascript_compressed.js'
+    `${BUILD_DIR}/blockly_compressed.js`,
+    `${BUILD_DIR}/msg/js/en.js`,
+    `${BUILD_DIR}/blocks_compressed.js`,
+    `${BUILD_DIR}/javascript_compressed.js`,
   ];
   return gulp.src(srcs)
-    .pipe(gulp.concat('blockly.min.js'))
-    .pipe(gulp.dest(`${packageDistribution}`))
+      .pipe(gulp.concat('blockly.min.js'))
+      .pipe(gulp.dest(`${RELEASE_DIR}`));
 };
 
 /**
- * This task copies all the media/* files into the distribution directory.
+ * This task copies all the media/* files into the release directory.
  */
 function packageMedia() {
-  return gulp.src('./media/*')
-    .pipe(gulp.dest(`${packageDistribution}/media`));
+  return gulp.src('media/*')
+    .pipe(gulp.dest(`${RELEASE_DIR}/media`));
 };
 
 /**
- * This task copies the package.json file into the distribution directory.
+ * This task copies the package.json file into the release directory.
  */
 function packageJSON(cb) {
   const packageJson = getPackageJson();
   const json = Object.assign({}, packageJson);
   delete json['scripts'];
-  if (!fs.existsSync(packageDistribution)) {
-    fs.mkdirSync(packageDistribution);
+  if (!fs.existsSync(RELEASE_DIR)) {
+    fs.mkdirSync(RELEASE_DIR);
   }
-  fs.writeFileSync(`${packageDistribution}/package.json`,
+  fs.writeFileSync(`${RELEASE_DIR}/package.json`,
       JSON.stringify(json, null, 2));
   cb();
 };
 
 /**
- * This task copies the scripts/package/README.md file into the distribution directory.
- * This file is what developers will see at https://www.npmjs.com/package/blockly.
+ * This task copies the scripts/package/README.md file into the
+ * release directory.  This file is what developers will see at
+ * https://www.npmjs.com/package/blockly .
  */
 function packageReadme() {
-  return gulp.src('./scripts/package/README.md')
-    .pipe(gulp.dest(`${packageDistribution}`));
+  return gulp.src('scripts/package/README.md')
+    .pipe(gulp.dest(RELEASE_DIR));
 };
 
 /**
- * This task copies the typings/blockly.d.ts TypeScript definition file into the
- * distribution directory.
- * The bundled declaration file is referenced in package.json in the types property.
+ * This task copies the typings/blockly.d.ts TypeScript definition
+ * file into the release directory.  The bundled declaration file is
+ * referenced in package.json in the types property.
  */
 function packageDTS() {
-  return gulp.src(['./typings/*.d.ts', './typings/msg/*.d.ts'], {base: './typings'})
-    .pipe(gulp.dest(`${packageDistribution}`));
+  const handwrittenSrcs = [
+    'typings/*.d.ts',
+    '!typings/blockly.d.ts',  // Exclude checked-in copy of blockly.d.ts.
+    'typings/msg/msg.d.ts',
+  ];
+  const builtSrcs = [
+    `${BUILD_DIR}/blockly.d.ts`,  // Use freshly-built one instead.
+    `${BUILD_DIR}/msg/*.d.ts`,
+  ];
+  return gulp.src(handwrittenSrcs, {base: 'typings'})
+      .pipe(gulp.src(builtSrcs, {base: BUILD_DIR}))
+      .pipe(gulp.dest(RELEASE_DIR));
 };
 
 /**
- * This task prepares the NPM distribution files under the /dist directory.
+ * This task cleans the release directory (by deleting it).
  */
-const package = gulp.parallel(
-  packageIndex,
-  packageSources,
-  packageCompressed,
-  packageBrowser,
-  packageNode,
-  packageCore,
-  packageNodeCore,
-  packageBlockly,
-  packageBlocks,
-  packageJavascript,
-  packagePython,
-  packageLua,
-  packageDart,
-  packagePHP,
-  packageLocales,
-  packageMedia,
-  packageUMDBundle,
-  packageJSON,
-  packageReadme,
-  packageDTS
-);
+function cleanReleaseDir(done) {
+  // Sanity check.
+  if (RELEASE_DIR === '.' || RELEASE_DIR === '/') {
+    throw new Error(`Refusing to rm -rf ${RELEASE_DIR}`);
+  }
+  rimraf(RELEASE_DIR, done);
+}
+
+/**
+ * This task prepares the files to be included in the NPM by copying
+ * them into the release directory.
+ */
+const package = gulp.series(
+    checkBuildDir,
+    cleanReleaseDir,
+    gulp.parallel(
+        packageIndex,
+        packageSources,
+        packageCompressed,
+        packageBrowser,
+        packageNode,
+        packageCore,
+        packageNodeCore,
+        packageBlockly,
+        packageBlocks,
+        packageJavascript,
+        packagePython,
+        packageLua,
+        packageDart,
+        packagePHP,
+        packageLocales,
+        packageMedia,
+        packageUMDBundle,
+        packageJSON,
+        packageReadme,
+        packageDTS)
+    );
 
 module.exports = {
+  cleanReleaseDir: cleanReleaseDir,
   package: package,
 };
diff --git a/scripts/gulpfiles/release_tasks.js b/scripts/gulpfiles/release_tasks.js
index 5e14fc08c..793ce50d3 100644
--- a/scripts/gulpfiles/release_tasks.js
+++ b/scripts/gulpfiles/release_tasks.js
@@ -17,9 +17,9 @@ var typings = require('./typings');
 var buildTasks = require('./build_tasks');
 var gitTasks = require('./git_tasks');
 var packageTasks = require('./package_tasks');
-var { getPackageJson } = require('./helper_tasks');
+var {getPackageJson} = require('./helper_tasks');
+var {RELEASE_DIR} = require('./config');
 
-const RELEASE_DIR = 'dist';
 
 // Gets the current major version.
 function getMajorVersion() {
@@ -80,20 +80,25 @@ function checkBranch(done) {
 }
 
 
-// Sanity check that the dist folder exists, and that certain files are in the dist folder.
-function checkDist(done) {
-  const sanityFiles = ['blockly_compressed.js', 'blocks_compressed.js', 'core', 'blocks', 'generators'];
-  // Check that dist exists.
+// Sanity check that the RELASE_DIR directory exists, and that certain
+// files are in it.
+function checkReleaseDir(done) {
+  const sanityFiles = ['blockly_compressed.js', 'blocks_compressed.js',
+                       'core', 'blocks', 'generators'];
+  // Check that directory exists.
   if (fs.existsSync(RELEASE_DIR)) {
-    // Sanity check that certain files exist in dist.
+    // Sanity check that certain files exist in RELASE_DIR.
     sanityFiles.forEach((fileName) => {
       if (!fs.existsSync(`${RELEASE_DIR}/${fileName}`)) {
-        done(new Error(`Your dist folder does not contain:${fileName}`));
+        done(new Error(
+            `Your ${RELEASE_DIR} directory does not contain ${fileName}`));
+        return;
       }
     });
     done();
   } else {
-    done(new Error('The dist directory does not exist. Is packageTasks.package being run?'));
+    done(new Error(`The ${RELEASE_DIR} directory does not exist.  ` +
+        'Has packageTasks.package been run?'));
   }
 }
 
@@ -144,36 +149,46 @@ function updateBetaVersion(done) {
   done();
 }
 
+// Build Blockly and prepare to check in the resulting built files.
+const rebuildAll = gulp.series(
+  buildTasks.cleanBuildDir,
+  buildTasks.build,
+  buildTasks.checkinBuilt,
+  typings.typings,
+  typings.checkinTypings,
+  );
+
 // Package and publish to npm.
 const publish = gulp.series(
+  rebuildAll,
   packageTasks.package,
   checkBranch,
-  checkDist,
+  checkReleaseDir,
   loginAndPublish
 );
 
 // Publish a beta version of Blockly.
 const publishBeta = gulp.series(
   updateBetaVersion,
-  buildTasks.build,
+  rebuildAll,
   packageTasks.package,
   checkBranch,
-  checkDist,
+  checkReleaseDir,
   loginAndPublishBeta
 );
 
-// Switch to a new branch, update the version number, and build Blockly.
-const recompile = gulp.series(
+// Switch to a new branch, update the version number, build Blockly
+// and check in the resulting built files.
+const recompileDevelop = gulp.series(
   gitTasks.syncDevelop(),
   gitTasks.createRebuildBranch,
   updateVersionPrompt,
-  buildTasks.build,
-  typings.typings,
+  rebuildAll,
   gitTasks.pushRebuildBranch
   );
 
 module.exports = {
-  recompile: recompile,
+  recompile: recompileDevelop,
   publishBeta: publishBeta,
   publish: publish
 }
diff --git a/scripts/gulpfiles/typings.js b/scripts/gulpfiles/typings.js
index 67b94f59c..4f4a82845 100644
--- a/scripts/gulpfiles/typings.js
+++ b/scripts/gulpfiles/typings.js
@@ -16,6 +16,7 @@ var path = require('path');
 var fs = require('fs');
 var rimraf = require('rimraf');
 var execSync = require('child_process').execSync;
+var {BUILD_DIR} = require('./config');
 
 /**
  * Recursively generates a list of file paths with the specified extension
@@ -94,7 +95,7 @@ function typings() {
   ];
   return gulp.src(srcs)
     .pipe(gulp.concat('blockly.d.ts'))
-    .pipe(gulp.dest('typings'))
+    .pipe(gulp.dest(BUILD_DIR))
     .on('end', function () {
       // Clean up tmp directory.
       if (fs.existsSync(tmpDir)) {
@@ -110,12 +111,24 @@ function msgTypings(cb) {
   msgFiles.forEach(msg => {
     const localeName = msg.substring(0, msg.indexOf('.json'));
     const msgTypings = template.slice().replace(/<%= locale %>/gi, localeName);
-    fs.writeFileSync(path.join('typings', 'msg', localeName + '.d.ts'), msgTypings, 'utf-8');
+    fs.writeFileSync(path.join(BUILD_DIR, 'msg', localeName + '.d.ts'), msgTypings, 'utf-8');
   })
   cb();
 }
 
+/**
+ * This task copies built files from BUILD_DIR back to the repository
+ * so they can be committed to git.
+ */
+function checkinTypings() {
+  return gulp.src([
+    `${BUILD_DIR}/**.d.ts`,
+    `${BUILD_DIR}/**/**.d.ts`,
+  ]).pipe(gulp.dest('typings'));
+};
+
 module.exports = {
   typings: typings,
-  msgTypings: msgTypings
+  msgTypings: msgTypings,
+  checkinTypings: checkinTypings,
 };
diff --git a/tests/run_all_tests.sh b/tests/run_all_tests.sh
index 5107a6ebf..f6c7c0f8c 100755
--- a/tests/run_all_tests.sh
+++ b/tests/run_all_tests.sh
@@ -51,14 +51,15 @@ run_test_command () {
 # Lint the codebase.
 run_test_command "eslint" "eslint ."
 
-# Run the closure compiler.
-run_test_command "compile" "npm run build"
+# Run the full usual build process.
+run_test_command "build" "npm run build"
 
-# Run the closure compiler ensuring there are no compiler warnings / errors.
-run_test_command "compile:warnings" "npm run build:debug"
+# Run the debug build, to ensure there are no closure compiler
+# warnings / errors.
+run_test_command "build:debug" "npm run build:debug"
 
 # Generate TypeScript typings and ensure there are no errors.
-run_test_command "typings" "tests/scripts/compile_typings.sh"
+run_test_command "typings" "npm run typings"
 
 # Check the sizes of built files for unexpected growth.
 run_test_command "metadata" "tests/scripts/check_metadata.sh"
@@ -69,6 +70,9 @@ run_test_command "mocha" "node tests/mocha/run_mocha_tests_in_browser.js"
 # Run generator tests inside a browser and check the results.
 run_test_command "generators" "tests/scripts/run_generators.sh"
 
+# Run the package build process, as Node tests depend on it.
+run_test_command "package" "npm run package"
+
 # Run Node tests.
 run_test_command "node" "./node_modules/.bin/mocha tests/node --config tests/node/.mocharc.js"
 
diff --git a/tests/scripts/check_metadata.sh b/tests/scripts/check_metadata.sh
index 8dbae6ccc..a35257c8e 100755
--- a/tests/scripts/check_metadata.sh
+++ b/tests/scripts/check_metadata.sh
@@ -1,9 +1,19 @@
 #!/bin/bash
 
 # Checks the size of generated files and verifies they aren't growing
-# unreasonably.
+# unreasonably.  Assumes the compressed files have already been built.
 
-# These values should be updated with each release
+# The ..._EXPECTED values should be updated with each release.
+# Run this script to get the new values.
+
+# Location of the pre-built compressed files.
+#
+# (TODO(#5007): Should fetch this from scripts/gulpfiles/config.js
+# instead of hardcoding it here.
+readonly BUILD_DIR='build'
+
+# These values should be updated with each release.  (Note that the
+# historic values are tab-delimited.)
 
 # Size of blockly_compressed.js
 # Q2 2019	2.20190722.0	812688
@@ -12,9 +22,10 @@
 # Q1 2020	3.20200402.0	619341
 # Q2 2020	3.20200625.0	621811
 # Q3 2020	3.20200924.0	641216
-# Q4 2020   4.20201217.0    653624
-# Q1 2021   5.20210325.0    653957
-blockly_size_expected=653957
+# Q4 2020	4.20201217.0	653624
+# Q1 2021	5.20210325.0	653957
+# Q2 2021	6.20210701.0	664497
+readonly BLOCKLY_SIZE_EXPECTED=664497
 
 # Size of blocks_compressed.js
 # Q2 2019	2.20190722.0	75618
@@ -23,9 +34,10 @@ blockly_size_expected=653957
 # Q1 2020	3.20200402.0	75805
 # Q2 2020	3.20200625.0	76360
 # Q3 2020	3.20200924.0	76429
-# Q4 2020   4.20201217.0    76693
-# Q1 2021   5.20210325.0    76693
-blocks_size_expected=76693
+# Q4 2020	4.20201217.0	76693
+# Q1 2021	5.20210325.0	76693
+# Q2 2021	6.20210701.0	76669
+readonly BLOCKS_SIZE_EXPECTED=76669
 
 # Size of blockly_compressed.js.gz
 # Q2 2019	2.20190722.0	180925
@@ -34,9 +46,10 @@ blocks_size_expected=76693
 # Q1 2020	3.20200402.0	134133
 # Q2 2020	3.20200625.0	135181
 # Q3 2020	3.20200924.0	138003
-# Q4 2020   4.20201217.0    138115
-# Q1 2021   5.20210325.0    136118
-blockly_gz_size_expected=136118
+# Q4 2020	4.20201217.0	138115
+# Q1 2021	5.20210325.0	136118
+# Q2 2021	6.20210701.0	142112
+readonly BLOCKLY_GZ_SIZE_EXPECTED=142112
 
 # Size of blocks_compressed.js.gz
 # Q2 2019	2.20190722.0	14552
@@ -45,49 +58,55 @@ blockly_gz_size_expected=136118
 # Q1 2020	3.20200402.0	14966
 # Q2 2020	3.20200625.0	15195
 # Q3 2020	3.20200924.0	15231
-# Q4 2020   4.20201217.0    15224
-# Q1 2021   5.20210325.0    15285
-blocks_gz_size_expected=15285
+# Q4 2020	4.20201217.0	15224
+# Q1 2021	5.20210325.0	15285
+# Q2 2021	6.20210701.0	15275
+readonly BLOCKS_GZ_SIZE_EXPECTED=15275
 
 # ANSI colors
-BOLD_GREEN='\033[1;32m'
-BOLD_RED='\033[1;31m'
-ANSI_RESET='\033[0m'
+readonly BOLD_GREEN='\033[1;32m'
+readonly BOLD_RED='\033[1;31m'
+readonly ANSI_RESET='\033[0m'
 
-# Build the compressed files for core and blocks
-echo "Building files"
-npm install
-gulp buildCompressed
-gulp buildBlocks
+# Terminate immediately with non-zero status if any command exits
+# with non-zero status, printing a nice message.
+set -e
+function fail {
+  echo -e "${BOLD_RED}Error while checking metadata.${ANSI_RESET}" >&2
+}
+trap fail ERR
 
-# GZip them for additional size comparisons
+# GZip them for additional size comparisons (keep originals, force
+# overwite previously-gzipped copies).
 echo "Zipping the compressed files"
-gzip -c blockly_compressed.js > blockly_compressed.js.gz
-gzip -c blocks_compressed.js > blocks_compressed.js.gz
+gzip -kf "${BUILD_DIR}/blockly_compressed.js"
+gzip -kf "${BUILD_DIR}/blocks_compressed.js"
 
 # Check the sizes of the files
 
 has_failed=0
 
 compare_size() {
-	local name=$1
-	local expected=$2
-	local compare=$(echo "$expected * 1.1 / 1" | bc)
+  local name="$1"
+  local expected="$2"
+  local compare=$(echo "${expected} * 1.1 / 1" | bc)
 
-	local size=$(wc -c <"$name")
+  local size=$(wc -c <"${name}")
 
-	if (( $size > $compare))
-	then
-		echo -e "${BOLD_RED}Failed: Size of $name has grown more than 10%. $size vs $expected ${ANSI_RESET}" >&2
-  		has_failed=1
-  	else
-  		echo -e "${BOLD_GREEN}Size of $name at $size compared to previous $expected.${ANSI_RESET}"
-  	fi
+  if (( $size > $compare))
+  then
+    echo -ne "${BOLD_RED}Failed: Size of ${name} has grown more than 10%. " >&2
+    echo -e "${size} vs ${expected} ${ANSI_RESET}" >&2
+    has_failed=1
+  else
+    echo -ne "${BOLD_GREEN}Size of ${name} at ${size} compared to previous " >&2
+    echo -e "${expected}.${ANSI_RESET}"
+  fi
 }
 
-compare_size "blockly_compressed.js" $blockly_size_expected
-compare_size "blocks_compressed.js" $blocks_size_expected
-compare_size "blockly_compressed.js.gz" $blockly_gz_size_expected
-compare_size "blocks_compressed.js.gz" $blocks_gz_size_expected
+compare_size "${BUILD_DIR}/blockly_compressed.js" $BLOCKLY_SIZE_EXPECTED
+compare_size "${BUILD_DIR}/blocks_compressed.js" $BLOCKS_SIZE_EXPECTED
+compare_size "${BUILD_DIR}/blockly_compressed.js.gz" $BLOCKLY_GZ_SIZE_EXPECTED
+compare_size "${BUILD_DIR}/blocks_compressed.js.gz" $BLOCKS_GZ_SIZE_EXPECTED
 
 exit $has_failed
diff --git a/tests/scripts/compile_typings.sh b/tests/scripts/compile_typings.sh
index ee16beb56..35e9d56dc 100755
--- a/tests/scripts/compile_typings.sh
+++ b/tests/scripts/compile_typings.sh
@@ -1,13 +1,23 @@
 #!/bin/bash
 
+# Location that npm run typings will write .d.ts files to.
+#
+# (TODO(#5007): Should fetch this from scripts/gulpfiles/config.js
+# instead of hardcoding it here.
+readonly BUILD_DIR='build'
+
 # ANSI colors
 BOLD_GREEN='\033[1;32m'
 BOLD_RED='\033[1;31m'
 ANSI_RESET='\033[0m'
 
-# Download TypeScript to obtain the compiler.
-echo "Downloading TypeScript"
-npm install typescript
+# Terminate immediately with non-zero status if any command exits
+# with non-zero status, printing a nice message.
+set -e
+function fail {
+  echo -e "${BOLD_RED}Failed to compile TypeScript typings.${ANSI_RESET}" >&2
+}
+trap fail ERR
 
 # Generate Blockly typings.
 echo "Generating Blockly typings"
@@ -15,15 +25,8 @@ npm run typings
 
 # Use the TypeScript compiler to compile the generated typings.
 echo "Compiling typings"
-cd typings
+
+cd "${BUILD_DIR}"
 ../node_modules/.bin/tsc blockly.d.ts
 
-
-if [ $? -eq 0 ]
-then
-  echo -e "${BOLD_GREEN}TypeScript typings compiled successfully.${ANSI_RESET}"
-  exit 0
-else
-  echo -e "${BOLD_RED}Failed to compile TypeScript typings.${ANSI_RESET}" >&2
-  exit 1
-fi
+echo -e "${BOLD_GREEN}TypeScript typings compiled successfully.${ANSI_RESET}"